1. Technical Field
The present invention relates to high strength structural panels useful for applications including the building construction of roofs, floors, walls, doors and other structures where a high strength-to-density ratio and improved fire retardant characteristics are useful. More particularly, the present invention relates to the use of carbon foam in structural insulated panels which are highly resistant to heat, moisture, and other environmental stresses while maintaining an extremely high compressive strength.
2. Background Art
Many residential units' structures are built with a combination of lumber materials and metal nails. After construction of the structural frame, an insulating material such as fiberglass insulation is installed to control thermal conduction from the exterior of the residence to the interior. Also, an interior paneling, often comprising gypsum board is used to maintain the placement of the fiberglass insulation between the exterior wall and the interior surface. While this type of building structure is well understood and possesses adequate strength, this approach is both slow and labor intensive. Furthermore, these structures maintain poor insulation and resistance to environmental stresses such as moisture or insects. As such, Structural Insulated Panels (SIPs) have been gaining popularity for use as structural building materials. Essentially, outer high-strength layers are attached to an insulating inner layer, creating a sandwich layer possessing both strength and insulating properties. For example, in Smith, U.S. Pat. No. 4,163,349, discloses an insulated building, though without adequate thermal insulating properties.
In Hardcastle et al. (U.S. Pat. No. 4,425,396) an insulating panel is disclosed with a synthetic organic polymeric foam with protective weathering layers comprised of multiple thermoplastic sheets.
Cahill (U.S. Pat. No. 6,656,858) describes a lightweight laminate wall comprised of a low density layer of from about 0.5 to 3 pounds per cubic foot and a second, reinforcing layer of a polymeric fabric. These structures are lightweight, have a low moisture resistance and meet building code requirements regarding transverse wind loading.
Porter (U.S. Pat. No. 6,599,621) describes a SIP with high strength and resistance to fire and particularly to water and changes in humidity. The disclosed structures are comprised of an inner insulating core with a gypsum fiberboard on one face of the insulating core and an oriented strand board on the second face of the insulating core. Preferably, the insulating core is comprised of a plastic foam such as expanded polystyrene or urethane which is bonded to both the gypsum fiberboard and the oriented strand board.
Porter (U.S. Pat. No. 6,588,172) describes the incorporation of a laminated layer of plastic impregnated paper into a SIP to increase the panel's tensile strength while rendering it impervious to moisture. This layer is typically situated between the gypsum board and plastic foam core, adhered through a conventional bonding agent.
Parker (U.S. Pat. No. 4,628,650) describes a SIP with a foam core with a layer having an overhang projecting from the foam core edges. The overhang is situated to facilitate an effective seal between adjacent SIPs, providing better thermal insulation. Additionally, the core of the panels has channels through the structure for the placement of joists, studs or rafters.
Clear (U.S. Pat. No. 6,079,175) describes a SIP of cementitious material for building structures. A lightweight fill material such as bottom ash, cement and water is poured between spaces of two outermost ribs, which is claimed to provide insulation, strength and also rigidity to the panel and therefore the structure the panel comprises. This SIP has the advantage of being constructed in remote or more barren areas as it is fairly inexpensive to create.
Pease (U.S. Pat. No. 6,725,616) prepares an insulated concrete wall either cast or built with blocks which is attached to reinforced insulated strips. The patentee indicates that users will require less time and labor in making insulated using the patentee's method of fixing reinforced rigid foam to the surface of a concrete wall.
Pease (U.S. Pat. No. 6,892,507) describes a method and apparatus for making an SIP with a rigid foam sheet. The rigid foam sheets have multiple grooves in which reinforcing strips are situated. The strips and rigid foam are then covered and bonded with a reinforcing sheet, the sheet providing both structural support and moisture retention.
Unfortunately, SIPs produced by the prior art are not effective for many structural applications requiring high strength including high compressive strength values. Furthermore, most SIPs claimed throughout the prior art are not effective against high heat or open flames, either combusting or experiencing significant charring. In addition, the prior art SIPs generally lack a high strength to density ratio, making such SIPs ill suited for applications where a lightweight, insulating, yet strong panel is necessary for a building structure.
What is desired, therefore, is structural panel which is of a low density and has desirable thermal insulating properties, where the panel has a high strength and high strength to density ratio making the carbon foam structural insulated panel useful for structural applications including roofs, floors, doors, and walls. Indeed, a combination of characteristics, including strength to density ratios and compressive strength higher than contemplated in the prior art, as well as fire retardancy higher than contemplated in the prior art, have been found to be necessary for structural applications not limited to residential buildings, commercial buildings, aircraft or watercraft.